Centrifugal switch



R. W. PATTERSON CENTRIFUGAL SWITCH Filed Dec. l, 1953 RogerWPale/rsonINVENTOR.

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lMay 10, 1960 United States Patent CENTRIFUGAL SWITCH ApplicationDecember 1, 1953, Serial No. '395,631

2 Claims. (Cl. 200-80) This invention relates to an improved centrifugalswitch adapted to control an electrical circuit whenever the speed ofrotation of the member to which it is attached reaches a predeterminedValue.

Centrifugal switches have been previously known which were intended toattain these same results. However, such switchesjhave been found to beunduly sensitive to acceleration forces and vibration to which the unitmay be subjected during its normal course of operation. As a result, theaction of such prior art switches is vnot positive and there is found tobe a considearble variation in the point at which the switch will beactuated.

It is, therefore, an object of this invention to provide a centrifugalswitch which will be actuated at substantially thesame predeterminedrate of rotation regardless of the accelerations involved.

A further object is to provide such a switch which will be actuated tomake or break the associated electrical circuit quickly and positivelyregardless of accelerations or vibrations to which it may be subjectedat the time when the .predetermined speedof rotation is reached.

A still further object is to provide such a switch which isextremelyrugged, of simple construction, and relatively inexpensive tomanufacture.

Further objects will become apparent from the following specilicationand claims, especially when considered in the light of the accompanyingdrawing.

Fig. 1 is a perspective view of the centrifugal switch with parts brokenaway to show the interior construction.

Fig. 2 is an end view of the switch, also with portions broken away toshow certain details of the construction.

Fig. 3 is a fragmentary sectional view taken generally in the planeindicated by line 3--3 of Fig. 2.

As best shown in Fig. 1, the `switch includes a shaft 1 having anoutwardly extending ilange 2 at the end thereof to which the main switchbody 3, of insulating material such as polystyrene, is suitablyattached. As shown in Figs. 1 and 2, the body 3 is cylindrical in formand is mounted coaxially with the shaft 1. Suitably secured to the outerperiphery of the body 3 lis a cylindrical ring 4 of metal which, ashereinafter described, may conveniently serve as a slip ring forconducting electric current to the switch assembly.

Extending diametrically through the body 3 is a bore 5, one end portionof which is internally threaded, as indicated at 6. A cylindrical guidesleeve 7 is arranged to be screwed into the threaded portion of the boreand is provided at its lower or inner end with an outwardly extendingange 8, the .periphery of which is serrated, as indicated at 9. As willbe later described, the radial position of sleeve 7 in bore 5 may beadjusted by screwing it in or out of the bore so as to set the speed atwhich the switch will be actuated to the desired value. Sleeve 7 is heldin its adjusted position by means of a generally L-shaped spring lockingmember 10, the inner end portion 11 of which extends generally axiallyinwardly through a suitable slot 12 formed in the body 3 and intoengagement with the serrated ange 8 of the sleeve, The

. Patented May 10, j 1960 2 other end of the locking member 10 issecured to the body 3 by means of a bolt 13 which, as shown in Fig. 3,may conveniently extend through the body and into threaded engagementwith the ilange 2. Thus, the spring lock and the bolt serve theadditional purpose of providing an electrical connection from the switchmechanism to the shaft 1. j

The lower or inner end of the opening through the sleeve 7 is arrangedto be closed by a suitable stop member 14 held thereagainst at all timesby a compression spring 15. Spring 15 abuts'a-gainst a suitabledisk-like member 16 of insulating material, inserted into the lower endof the bore between the spring and the inner periphery of the ring 4.

Slidably guided within sleeve 7 is a metal plunger or weight 17 which isrestrained against all but radial movement by means of the bearingsurfaces afforded by the inwardly flange 18 on the upper end ofthesleeve 7 and the outwardly extending ange 19 on the lower end of theplunger 17. A compression spring 20 acting betweenv the flanges 18 and19 normally, urges the plunger against the stop 14 and serves to opposeradial outward movement of the plunger 17 under the action ofcentrifugal force. Plunger 17 is preferably provided at its outer endwith a contact button 21 of low resistance contact material.

Ring 4 is provided on its inner periphery with a groove 22 within whichis suitably secured a resilient contact member 23 which, as best shownin Fig. 2, extends into position directly opposite, and normally spacedfrom, the contact button 21 on the plunger 17. Thus when the plungermoves outwardly into engagement with contact member 23, an electricalcircuit will be completed from shaft 1, through flange Z, bolt 13,spring lock member 10, sleeve 7, plunger 17, and contact member 23 tothe slip ring 4. Suitable brushes (not shown) may be associated with theslipring 4 and the shaft 1 to connect the switch to the external circuitto be controlled.

Spring 20 is so chosen that it will be preloaded when inserted betweenthe flanges Y18 and 19 with the parts in their normal position shown inFig. l with-the plunger 17 .engaged against the stop 14. Sleeve 7 is sopositioned in boreV 5 rthat under normal conditions, the center ofgravity of the plunger 17 will be displaced radially outwardly from theaxis of the shaft 1 so that, upon rotation of the shaft, the plunger 17will tend to move radially outwardly by centrifugal action against theaction of spring 20. The preloading of spring 20 and the degree ofeccentricity of the center of gravity of plunger 17 relative to the axisof the shaft are so related that, until the predetermined desired speedof operation of the switch is reached, radial outward movement of theplunger will be prevented by the spring '20. However, as soon as thepredetermined speed is attained, plunger 17 will move radially outwardlyand into contact with spring contact member 23 to complete theabove-mentioned electrical circuit. The speed of rotation at which theswitch will be actuated may be set at the desired point by bodilyshifting the sleeve 7 axially of the bore as previously described, thusvarying the radial eccentricity of the center j of gravity of theplunger 17 with respect to the axis of the shaft 1.

An important feature of this invention resides in the characteristics ofthe spring 20. Not only is this spring preloaded, as described above, toprevent movement of the plunger until the desired speed of rotation isattained, but moreover the spring rate of the spring 20 is so related tothe mass of the plunger 17 that, upon rotation of the shaft above thepredetermined rate, the rate of increase in force exerted by this springagainst the plunger due to outward movement thereof will be less thanthe corresponding rate of increase of the centrifugal force actingthereon as a result of such movement. Thus, the plunger will be held inits normal position until the desired speed is attained and will thensuddenly fly radially outwardly into engagement with the spring contact23. Thus, a snap action will result which will insure a quick andpositive closing of the circuit. The spring contact 23 will readilyabsorb the impact while maintaining the desired positive contact andmoreover will follow any slight uctuations in the position of theplunger resulting from vibrations to which the switch unit may besubjected. Similar snap action will be obtained when the speed ofrotation again falls below the predetermined speed since, as soon as theplunger begins to move radially inwardly, the centrifugal force willfall off at a more rapid rate than the force exerted by the spring 2t).

Where it is desired that the difference between the speeds of rotationat which the switch will close and open be kept at a minimum, the springrate should be chosen so that the difference between the force exertedagainst the plunger by the spring and the centrifugal force increasesbut slightly as the plunger moves outwardly while still maintainingenough difference to insure the snap action. Obviously, too heavy aspring will entirely prevent the snap action and the plunger wouldmerely move slowly outwardly to a new equilibrium position as the speedincreased above the predetermined desired value. On the other hand, toolight a spring would give a very strong snap action but would result inan unduly wide difference between the speed at which the switch wouldclose and that at which it would open.

The operation of this switch is believed obvious from the foregoingdescription. Since all of the movable elements are arranged so that theycan move only along a radius, their action will be substantiallyindependent of the rate at which the shaft is accelerating orde-accelerating. Moreover, by adjusting the position of the sleeve, (andas a result, the position of the center of gravity of the plunger) theunit can be accurately adjusted to operate at the desired speed ofrotation of the shaft. The novel snap action results in positive openingand closing of the circuit being controlled and, together with the useof the resilient spring contract 23 minimizes any tendency for thecontacts to chatter when the unit is subjected to vibration.

hile but one form of the invention has been shown in detail, it isbelieved obvious that many changes in the specific construction andarrangement of the parts may be made without departing from theprinciple of operation or the scope of the invention as defined by theappended claims.

l2,936,352 Y r I claim:

l. A centrifugal switch comprising a shaft, a generally cylindrical bodymember of insulating material rigidly secured to said shaft coaxiallytherewith, said body being provided with a cylindrical bore extendingdiametrical- 1y therethrough, a sleeve of conducting material threadedlyengaged within said bore, means electrically connecting said sleeve tosaid shaft, a metal plunger carried within said sleeve with a slidingfit, a stop member slidable within said bore and adapted to abut againstthe inner end of said sleeve, a ring of conducting material secured tothe periphery of said body and covering the opposite ends of said bore,means including a compression spring interposed between said stop memberand the inner peripheral wall of said ring for holding said stop againstthe inner end of said sleeve, a second compression spring surroundingsaid plunger and acting between said sleeve and said plunger and urgingsaid plunger radially inwardly into a normal position against said stop,said sleeve being so positioned in said bore that when said plunger isin said normal position its center of gravity will be displaced radiallyfrom the axis of said body so that upon rotation of said bodycentrifugal force acting on said plunger will tend to move it radiallyoutwardly from said axis against the action of said second spring, and aresilient contact strap carried by the ring opposite the outer end ofsaid plunger and normally spaced therefrom, said contact being adaptedto be directly engaged by said plunger upon a predetermined radialoutward movement thereof to complete an electrical circuit from saidshaft to said ring.

2. A centrifugal switch as set forth in claim 1 wherein said secondspring is preloaded so as to prevent radial movement of said plungeruntil a predetermined rate of rotation of said body has been reached,said second spring having a spring rate so related to the mass of saidplunger that upon rotation of said member above said predetermined ratethe rate of increase in force exerted by said second spring against saidplunger due to outward movement of said plunger will be less than thecorresponding rate of increase of the centrifugal force acting thereonas a result of such movement.

References Cited in the tile of this patent UNITED STATES PATENTS1,075,987 McMahon Oct. 14, 1913 1,296,138 Taylor Mar. 4, 1919 2,387,788Wiles Oct. 30, 1945 2,747,854 Schnepf May 29, 1956

